Field of the Invention
The present invention relates to a motor driving apparatus, a sheet conveyance apparatus, a document feeding apparatus, a document reading apparatus and an image forming apparatus.
Description of the Related Art
In electrophotographic image forming apparatuses such as copiers and printers, motors such as stepping motors are widely used as a driving source of a conveyance system that conveys recording materials such as sheets of paper on which images are to be formed. In a case where a driving circuit such as an H bridge circuit that is constituted by a plurality of switching elements (FETs) is used to drive such a motor, the motor is driven by the FETs being controlled by PWM signals, and a driving current being supplied to the motor. In such a case, a driving current that flows through the winding of the motor is detected, and a PWM signal is generated based on the result of detection, and thus driving control, by which the value of the driving current that is to be supplied to the motor is controlled so as to be a target value, can be realized.
In a configuration in which an H bridge circuit is used as a driving circuit for a motor, the driving current that flows through the winding of the motor can be detected based on, for example, the current that flows through a current detection resistor that is arranged on the ground side of the H bridge circuit. U.S. Pat. No. 5,574,344 discusses a configuration in which the driving current that flows through the winding of the motor is detected by using a resistor that is arranged on the ground side of the H bridge circuit, and in which the driving current that flows through the winding of the motor is detected by reversing the polarity (sign), which is positive or negative, of the voltage across the two ends of the resistor in synchronization with a PWM signal.
In the case of driving a motor by using the above-described driving circuit or the like, there is the possibility of the result of detection of the driving current being distorted due to the transient response properties of the driving current that flows through the winding (coil) of the motor, in response to the PWM signal supplied to the driving circuit. Specifically, the current value that is detected varies depending on whether the driving current is detected during a period in which the PWM signal is at an H level or during a period in which the PWM signal is at an L level. As a result, the current waveform that indicates the result of detection of the driving current is distorted, and there is the possibility of a failure occurring in motor driving control that is performed based on the result of detection.